After having owned this lens for about a month now, the lens fell over while standing on a short tripod for macro purposes. The lens fell on the grass and broke right through the middle!
The plastic back part of the lens is fixed to a metal front frame by means of 3 really tiny screws. These screws are embedded in the plastic. This really is a very weak construction!
Take a look at these images:http://www.markdal.com/sigma1.jpghttp://www.markdal.com/sigma2.jpg